This invention relates to a heat transfer control system for controlling temperature and temperature gradient related defects generated in a crystal during growth by regulating thermal stress in the growing crystal.
Recent advances in high performance integrated circuit technologies have resulted in increased demand for high quality, large diameter semi-insulating material such as gallium arsenide, GaAs. Gallium arsenide is a III-V semiconductor material referring to the groups to which gallium and arsenic belong in the Periodic Table.
The primary crystalline defect in III-V semiconductor crystals grown by the LEC (liquid encapsulated Czochralski) technique is the presence of massive dislocation networks resulting from excessive thermal stresses experienced by the crystal solid during growth. Significant reduction in the density of dislocation is required for improved performance of opto-electronic as well as digital and monolithic IC devices utilizing these crystals. It has been recognized for several years that reduction of thermal stress levels below the plasticity limit requires, in principle, a reduction of temperature gradients in the solid to below critical values. Known attempts to control temperature gradients in the solid involve control of the environmental temperature distribution surrounding the crystal during growth. The known techniques have not, however, resulted in the production of dislocation-free GaAs crystals having a diameter on the order of three inches.